1. Field of the Invention
The present invention relates to introducing catheters and specifically to such a catheter having a bevelled introducing tip, a cylindrical portion between the end of the bevel and a tapered portion. Visible indicia are provided on the introducing catheter, the indicia starting at the tip. The invention also relates to introducing sheaths having a bevelled introducing tip and visible indicia to locate the position of the bevel.
2. Description of the Prior Art
Insertion of catheters into blood vessels is frequently done by the percutaneous method, a procedure comprising a series of steps as follows:
(1) A needle punctures the skin and is directed into the blood vessel, such entry generally heralded by the back-flow of blood through said needle.
(2) A fine guide wire in the form of a tightly coiled helix is inserted within said needle, enters said blood vessel where it is advanced so that a portion lies securely within the blood vessel for some length while the remainder lies above the skin surface.
(3) The needle is withdrawn while the guide wire remains in place, partly within said blood vessel and extending proximally through the skin.
(4) A so-called introducnng or dilating catheter with tapered tip is threaded over the proximal end of the guide wire and advanced along the guide wire as its tip passes through the skin, subcutaneous tissue, and blood vessel wall to enter the lumen of the blood vessel continually guided by the flexible helical wire. The purpose of this introducing and/or dilating catheter is to expand the vascular puncture hole so that it will accommodate the operational diagnostic or therapeutic catheter to be finally inserted.
Introducing catheters presently in use are chosen with an outer diameter identical to that of the operational catheter, but the introducing catheter possesses a tip which tapers down to the outer diameter of the guide wire. The present art for such a tapered tip is exclusively that comprising a taper which is radially symmetrical. The taper involves both the lumen and the wall of the introducing-dilating catheter over a length of approximately 20 mm. Therefore, when passed over the guide wire into the blood vessel, a sufficient portion of he introducing-dilating catheter is inserted into the blood vessel so that the entire tapered tip as well as some portion of the full diameter of the catheter lies within said vessel, thereby insuring that the vascular puncture hole has been dilated to the full diameter of the catheter.
(5) A thin-walled outer tubular member, called a sheath, is passed over the proximal end of the introducing-dilating catheter, to whose diameter it fits precisely, and then the sheath and catheter are advanced through the skin, subcutaneous tissue and blood vessel wall until its distal portion of the sheath enters the lumen of said blood vessel.
(6) The introducing catheter and internal guide wire are quickly removed from the sheath while maintaining the position of the tubular sheath within the blood vessel, and the operational catheter is inserted via the sheath into the blood vessel, from whence it can be manipulated to other locations within the circulatory system.
Many patents have issued for apparatus relating to inserting and/or dilating catheters.
Thompson U.S. Pat. No. 3,921,631 shows a device for insertion of catheters using a hollow slotted needle. This is a so-called "through-the-needle" catheter insertion apparatus. The needle tip 20 is bevelled to form a cutting edge which results in a shearing or slicing action when forming the puncture hole rather than a tearing action, so as to produce a smooth puncture rather than a ragged puncture. A varying diameter tapered section is employed at the distal end of the catheter hub to seal the space between the needle and the catheter to prevent bleeding.
Suzuki et al. U.S. Pat. No. 4,629,450 discloses an instrument comprising an inner needle with a tip formed to include a cutting edge, and a dilator portion having a hollow dilator with a tip for enabling the inner needle to be passed therethrough until the cutting edge of the inner needle projects from the tip of the dilator. As discussed in the patent, the cutting tip of the inner needle makes the initial puncture of the vessel. The inner needle is then withdrawn leaving the dilator portion in place. A guide wire is then inserted through the dilator. A secondary thicker portion of the dilator is then inserted along the guide wire to widen the opening. The dilator is then withdrawn and the catheter is inserted over and along the guide wire.
Both of these patents deal with bevels of the initial puncturing member which are metallic needles. The present art for fabricating the tapered tip of an introducing-dilating catheter as used in (4) of the percutaneous method described above is exclusively that comprising a taper which is radially symmetrical, and ending in a tip cut off at a right angle to the longitudinal axis of the catheter. Although the wall of the catheter, as well as the lumen within, is tapered to present the smallest profile when engaging the puncture hole, the limited strength of the flexible plastic material of which these catheters are made necessarily limits the degree to which the wall can be thinned down. Hence, the catheter tip presents as a blunt step upon attempting to enter the puncture hole over the guide wire. Although, approaching the artery at an acute angle of approximately 35.degree., the elasticity of the blood vessel permits some movement of the vessel wall at the acute angle such that the entire blunt circumference of the catheter tip is pressing against the entire circumference of the puncture hole as force is applied to effect entry of the catheter. Often, the required force is considerable and the catheter generally pops through the puncture hole suddenly with a palpable abruptness. This may cause additional trauma or tearing at the puncture site.
This introducing problem is again encountered when positioning the sheath over the catheter within the lumen of the blood vessel.